This paper reports on a project to compare the representation of the semiannual oscillation (SAO) among six major global atmospheric reanalyses and with recent satellite observations. The differences among the zonal mean zonal wind as represented by the various reanalyses display a prominent equatorial maximum that increases with height. It is shown that assimilation of satellite temperature measurements is crucial for the realistic representation of the tropical upper stratospheric circulation.

This paper documents the numerical experiments to be used in phase 1 of the Stratosphere–troposphere Processes And their Role in Climate (SPARC) Quasi-Biennial Oscillation initiative (QBOi), which was set up to improve the representation of the QBO and tropical stratospheric variability in global climate models.

This paper compares the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis data sets. Differences among reanalysis display a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. Our study confirms that the high accuracy in situ wind measurements have provided important constraints to reanalyses of circulation in the tropical stratosphere.